350-501 Practice Test 12 — 15 Questions

Question 1

A customer requires MPLS Layer 2 VPN connectivity between two sites using Pseudowire. Which control protocol is used to signal the pseudowire label?

Accepted Answer

LDP. B is correct because LDP (Label Distribution Protocol) is the standard control protocol used to signal pseudowire labels in MPLS Layer 2 VPNs. Specifically, the Targeted LDP (T-LDP) session between the two Provider Edge (PE) routers exchanges the Virtual Circuit (VC) label, which is the inner label used to identify the pseudowire. This is defined in RFC 4447 and is the default signaling mechanism for AToM (Any Transport over MPLS).

Answer

RSVP-TE

Answer

BGP

Answer

OSPF

Question 2

Refer to the exhibit. This JSON policy is used for Segment Routing Traffic Engineering. What is the purpose of the 'color' attribute?

Accepted Answer

It identifies a specific SR-TE policy to be used for traffic steering. In Segment Routing Traffic Engineering (SR-TE), the 'color' attribute is a 32-bit numerical value that, combined with the destination prefix, uniquely identifies an SR-TE policy. This allows traffic to be steered into a specific policy based on color, enabling advanced traffic engineering use cases such as multi-topology routing or service-level agreement (SLA) differentiation.

Answer

It sets the metric type for the path calculation

Answer

It defines the preference value for the candidate path

Answer

It specifies the link affinity constraint for the path

Question 3

Which TWO protocols are supported by a BNG (Broadband Network Gateway) for subscriber session establishment? (Choose two)

Accepted Answer

PPPoE. PPPoE (A) is correct because a BNG terminates PPPoE sessions, using PPP negotiation (LCP, authentication via PAP/CHAP, IPCP) to establish and manage each subscriber session over Ethernet access networks. IPoE (DHCP) (B) is also correct because a BNG supports IPoE subscriber sessions where DHCP (with Option 82 or similar) is used to assign addresses and trigger session creation, often with per-subscriber policies. IPSec (C) is a security protocol suite for VPNs, not a subscriber session establishment method on a BNG. L2TP (D) is a tunneling protocol often used with LAC/LNS architectures, not a native BNG subscriber session type. PPPoA (E) is used over ATM access, not supported as a BNG subscriber session establishment protocol in this context.

Answer

IPSec

Answer

L2TP

Answer

PPPoA

Question 4

An engineer is configuring MPLS-TE FRR for link protection. Which of the following options describes a 1:1 protection scheme where a dedicated detour LSP is created for each protected LSP?

Accepted Answer

Detour LSP for each protected LSP. In MPLS-TE Fast Reroute (FRR), a 1:1 protection scheme means a dedicated detour LSP is created for each protected LSP. This provides per-LSP backup, ensuring that if a link fails, traffic is immediately switched to the detour tunnel. Option C correctly describes this exact mechanism, where each protected LSP has its own pre-established detour path.

Answer

Shared mesh protection

Answer

Bypass tunnel protecting multiple LSPs

Answer

Node protection bypass tunnel

Question 5

In an MPLS network using LDP, which statement correctly describes the label distribution behavior for a given FEC?

Accepted Answer

Labels are advertised unsolicited to all neighbors, and all labels are retained even if not used (liberal label retention).. LDP uses downstream unsolicited mode by default, where each LSR advertises labels for all FECs to all neighbors without being asked, and liberal label retention stores all received labels even if not currently used.

Answer

Labels are advertised only in response to a request from an upstream neighbor (downstream on demand).

Answer

Labels are advertised unsolicited but only the best label for each FEC is retained (conservative label retention).

Answer

Labels are advertised only when the LSR has an outgoing label for the FEC (ordered label distribution).

Question 6

An engineer configures an MPLS-TE tunnel with a bandwidth of 100 Mbps and an explicit path that avoids a specific link. Which RSVP message carries the Explicit Route Object (ERO) to signal the path?

Accepted Answer

PATH message. In RSVP-TE, the PATH message includes the ERO to specify the explicit route for the tunnel.

Answer

RESV Confirm message

Answer

PATH Tear message

Answer

RESV message

Question 7

In IS-IS, which TWO are types of Link State PDUs (LSPs)?

Accepted Answer

Level 2 LSP. In IS-IS, Link State PDUs (LSPs) come in two distinct flooding scopes: Level 1 LSPs, which are flooded only within a Level 1 area, and Level 2 LSPs, which are flooded within the Level 2 backbone. Option B (Level 2 LSP) is correct because it is the LSP type used to distribute Level 2 link-state information (TLVs) across the backbone. Option E (Level 1 LSP) is correct because it is the LSP type used to distribute Level 1 link-state information within a single IS-IS area. Options A (PSNP) and D (CSNP) are not LSPs at all; they are Sequence Numbers PDUs used to acknowledge and synchronize the link-state database, and they exist in both Level 1 and Level 2 forms. Option C (Hello LSP) is not a valid IS-IS PDU type; IS-IS uses IIH (IS-IS Hello) PDUs for neighbor discovery, not a 'Hello LSP'.

Answer

Partial Sequence Numbers PDU (PSNP)

Answer

Hello LSP

Answer

Complete Sequence Numbers PDU (CSNP)

Question 8

Refer to the exhibit. A network engineer configures a BGP route-map to set communities on routes advertised to a neighbor. After applying the configuration, the engineer checks the BGP table on the neighbor router and does not see the communities. What is the most likely reason?

Accepted Answer

The neighbor is missing the 'send-community' command. C is correct because BGP communities are not sent to a neighbor by default. Even if a route-map sets the community values correctly, the neighbor will not receive them unless the 'send-community' command is configured under the neighbor statement. This command enables the advertisement of the community attribute in BGP updates.

Answer

The prefix-list does not match the exact prefix

Answer

The community values are not in the format 'AA:NN'

Answer

The route-map needs to be applied inbound

Question 9

In the DiffServ model, which DSCP value is used for Expedited Forwarding (EF) to support voice traffic?

Accepted Answer

DSCP 46. In the DiffServ model, Expedited Forwarding (EF) is defined by DSCP 46 (binary 101110), which provides low-latency, low-jitter, low-loss treatment suitable for voice traffic. EF is specified in RFC 3246 and is the standard marking for VoIP bearer traffic. DSCP 46 is the correct value for EF.

Answer

DSCP 0

Answer

DSCP 40

Answer

DSCP 34

Question 10

An OSPF network uses point-to-point links. The engineer notices that LSAs are being flooded every 30 minutes even when no topology changes occur. What is the most likely reason?

Accepted Answer

The LSA refresh interval has expired.. In OSPF, LSAs have a default refresh interval of 30 minutes (1800 seconds). When this timer expires, the router that originated the LSA re-floods it to maintain database synchronization, even if no topology changes have occurred. This is normal OSPF behavior defined in RFC 2328, and it explains why LSAs are flooded every 30 minutes.

Answer

The routers are using LSU packets incorrectly.

Answer

There is a flapping interface on the network.

Answer

The dead timer is set too low.

Question 11

An engineer is implementing Unicast Reverse Path Forwarding (uRPF) on a provider edge (PE) router to mitigate IP spoofing. The customer-facing interface has a single static default route. Which uRPF mode should be used to provide anti-spoofing without causing false drops?

Accepted Answer

Loose mode. Loose mode uRPF checks that the source IP of a packet has a route in the FIB (any route, not necessarily via the receiving interface). Since the customer-facing interface has only a static default route, strict mode would drop legitimate traffic whose source is reachable via other paths. Loose mode provides anti-spoofing by ensuring the source is at least routable, without requiring the return path to match the ingress interface.

Answer

VRF mode

Answer

Strict mode

Answer

Feasible mode

Question 12

An engineer is designing an MPLS network and needs to ensure that VPN traffic between two PE routers is label-switched. The PE routers are connected via a P router and have a full mesh of iBGP sessions. Which label distribution method is required for the VPN labels?

Accepted Answer

MP-BGP. In MPLS VPN architectures, VPN labels (also known as service labels) are distributed using Multiprotocol BGP (MP-BGP). MP-BGP carries VPN-IPv4 routes that include both the route distinguisher (RD) and the VPN label in the Network Layer Reachability Information (NLRI). This allows PE routers to exchange per-VRF label bindings, enabling label-switched VPN traffic across the MPLS core. Without MP-BGP, the PE routers cannot signal the VPN-specific labels required for end-to-end label switching.

Answer

Segment Routing

Answer

RSVP-TE

Answer

LDP

Question 13

In SR-MPLS, what is the purpose of the SRGB (Segment Routing Global Block)?

Accepted Answer

To provide a global label space for prefix SIDs. The SRGB (Segment Routing Global Block) is a reserved range of MPLS labels that a node uses for global segments, specifically prefix SIDs. Each node advertises its SRGB, and prefix SIDs are computed as SRGB base + index, ensuring globally unique label values across the SR domain. This provides a consistent global label space for prefix segments.

Answer

To define the range of labels used for LDP

Answer

To reserve labels for MPLS-TE tunnels

Answer

To allocate labels for adjacency SIDs

Question 14

A service provider is deploying uRPF on peering edges with multiple upstream providers and asymmetric routing. Which two statements are true about uRPF operation in this scenario? (Choose two.)

Accepted Answer

Loose mode may drop traffic if no route to the source exists in the FIB. Option A is correct because loose-mode uRPF only verifies that a route back to the source address exists in the FIB, so if the source prefix is missing from the routing table the packet is dropped even though the return path need not match the incoming interface. Option D is correct because uRPF is supported for both IPv4 (ip verify unicast source reachable-via) and IPv6 (ipv6 verify unicast source reachable-via) on Cisco platforms, making it usable in dual-stack peering designs. Option B is wrong because uRPF depends on Cisco Express Forwarding and the FIB, so CEF must be enabled, not disabled. Option C is wrong because loose mode checks for a specific route to the source in the FIB; a default route alone does not satisfy the check unless it is the matching route. Option E is wrong because strict mode requires the return path to use the same interface the packet arrived on, which breaks in asymmetric routing, so loose mode is preferred there.

Answer

uRPF requires CEF to be disabled

Answer

Loose mode requires a default route to function

Answer

Strict mode is preferred for asymmetric routing environments

Question 15

An engineer is configuring MPLS LDP on a Cisco router. The router uses downstream unsolicited mode with liberal label retention. Which behavior describes the label distribution and retention on this router?

Accepted Answer

The router sends label bindings to all neighbors without receiving requests and retains all received label bindings.. Downstream unsolicited (DU) mode means an LSR distributes label bindings to all its LDP neighbors without waiting for a request. Liberal label retention means the LSR keeps all received label bindings, even those from non-best-path neighbors, rather than discarding them. Together, this describes a router that sends bindings unsolicited to all neighbors and retains all received bindings.

Answer

The router requests labels from neighbors and retains only labels for the best path.

Answer

The router sends label bindings only for directly connected routes and discards labels from non-reachable next hops.

Answer

The router sends label bindings only in response to requests from upstream neighbors and retains only labels for directly connected next hops.